The Australian Transport Safety Bureau (ATSB) has confirmed that missing Malaysia Airlines Flight MH370 is not in the search zone where acoustic pings were detected. / Rufus Cox, Getty Images

by Kim Hjelmgaard, USA TODAY

by Kim Hjelmgaard, USA TODAY

Acoustic signals thought to be linked to Malaysia Airlines Flight 370 have been ruled out as related to the final resting place of the vanished plane, investigators leading the search said Thursday.

The U.S. Navy's Bluefin 21 finished its final underwater mission in the southern Indian Ocean on Wednesday after scouring 330 square miles, the Australian-based Joint Agency Coordination Center said.

"The area can now be discounted as the final resting place of MH370," the JACC said in a statement.

The agency said that an expanded search of 21,600 square miles, based on satellite analysis of the plane's most likely route, would probably begin in August after commercial side-scan sonar operators are contracted.

That search is expected to last 12 months.

Earlier, U.S. Navy spokesman Chris Johnson dismissed comments made by ocean engineering expert Michael Dean to CNN that acoustic "pings" heard in the area in April did not come from the jet's black boxes. Dean had said those "pings" came from a source unrelated to the jet.

"Mike Dean's comments today were speculative and premature," Johnson said in a statement. Washington-based Dean could not be immediately reached for comment.

The plane carrying 227 passengers and 12 crew vanished on March 8 on a flight from Kuala Lumpur, Malaysia, to Beijing. Two-thirds of those traveling on the plane were from China.

On Tuesday, the Malaysian government made public 47 pages of raw satellite data used to conclude that the jet crashed into the southern Indian Ocean. Authorities believe the jet diverted sharply from its flight path and flew south to the Indian Ocean. But not a single piece of the missing Boeing 777 has been found in one of aviation's most baffling mysteries.